The structures of Mo/HZSM-5 catalysts with different molybdenum loadings were characterized and the reaction performances of methane dehydro-oligomerization over these catalysts were investigated. It was found that the BET surface areas, micropore volumes as well as the surface acidities of the catalysts decreased with the increasing of molybdenum loading. When the molybdenum loading was greater than 5%, molybdenum would impose significant influence on the crystalline structure of HZSM-5 zeolite and MoO3 phase would appear. The optimum molybdenum content for the conversion of methane to benzene and ethylene was about 2%. The synergisitc effect between molybdenum oxygen species and the acidic sites of HZSM-5 plays an important role in the catalysis conversion of methane as both MoO3 and HZSM-5 alone showed little reactivity. The molybdenum species were reduced and the acidic sites were covered by carbonaceous substances after the deactivation of catalysts. The carbon deposition seems to be the predominant reason for the catalyst deactivation because the catalyst activity could be rejuvenated after burning off coke.